Over the past twenty years, computer technology has evolved very rapidly. One aspect of this evolution has been a progressively growing demand for increased storage capacity in memory devices. In order to provide a high storage density at a reasonable cost, one of the most enduring techniques has been to provide a rotatable hard disk with a layer of magnetic material thereon, and a read/write head which is supported for movement adjacent the disk and can transfer information to and from the disk.
In an arrangement of this type, if airborne dust, smoke, vapors or other contaminants are present, they can be attracted to the disk by any electrostatic charge that may be present on the disk. Then, because the head is disposed closely adjacent to the disk during normal operation, the contaminants can be transferred to and progressively build up on the head. Eventually, the buildup of contaminants will be sufficient to interfere with the interaction between the head and disk, thereby increasing the error rate until the device will not operate.
In order to avoid this problem, most hard disk drives have the disk and head disposed within a sealed enclosure, so that the disk and head are not exposed to whatever airborne contaminants may happen to be present externally of the enclosure. This approach works well where the entire hard disk drive device is permanently installed in a computer. In other types of systems, however, a hard disk is provided within a removable cartridge, and it is desirable that the cartridge not include the read/write head.
In this regard, there are advantages to placing a head stack assembly (HSA) and its support structure within the drive which receives the cartridge, rather than in the cartridge. For example, a typical user will have several removable cartridges for each drive. Thus, in terms of overall system cost, it is cheaper to provide one head stack assembly with support which is in the drive, rather than to provide several head stack assemblies with support which are each disposed in a respective one of the many cartridges used with the drive. However, in removable cartridges, there is a problem in regard to keeping the head clean.
More specifically, in order to permit the head from the drive to access the disk within the cartridge, the cartridge is not provided with a sealed enclosure of the type discussed above. Instead, the cartridge is provided with an opening through which the head of the drive can be inserted into the cartridge. In some cases, a movable shutter is provided in order to obstruct the opening when the cartridge is not in the drive. However, when the cartridge is in the drive, the shutter moves to an open position. Thus, regardless of whether or not a shutter is present, when the cartridge is in the drive, there is an opening which gives the head access to the interior of the cartridge, and which also necessarily gives ambient air access to the interior of the cartridge, along with any dust, smoke, vapor or other contaminants that are carried by the ambient air.
Moreover, removable cartridges tend to be more susceptible to the effects of electrostatic charge. This is because, when a cartridge is not in a drive and is being manually handled, it is usually not in contact with any conductive material that can drain away charge that may build up on the exterior surface of the cartridge, and manual handling often has a tendency to cause a buildup of charge on the exterior surface of the cartridge housing. This charge on the exterior surface can in turn induce a buildup of charge within the housing, including a buildup of charge on the magnetic disk.
Consequently, since charge can build up on the disk and since the disk is exposed to contaminants in ambient air, the contaminants will tend to be attracted to and build up on the disk, and from there they will be transferred to and build up on the head during system operation. The effect of this contaminant buildup on the head can be ameliorated to some extent by keeping the storage density in the hard disk of a removable cartridge at a relatively low level, in comparison to the levels used for hard disks located within sealed enclosures. However, as mentioned above, the commercial marketplace is exhibiting a strong and progressively increasing demand for high-density storage in a removable cartridge.